N-terminal leucine/isoleucine/valine-binding protein (LIVBP)-like domain of the GluR5-7 subunits of Kainate receptor
N-terminal leucine/isoleucine/valine-binding protein (LIVBP)-like domain of the GluR5-7 subunits of Kainate receptor. While this N-terminal domain belongs to the periplasmic-binding fold type I superfamily, the glutamate-binding domain of the iGluR is structurally homologous to the periplasmic-binding fold type II. The LIVBP-like domain of iGluRs is thought to play a role in the initial assembly of iGluR subunits, but it is not well understood how this domain is arranged and functions in intact iGluR. There are five types of kainate receptors, GluR5, GluR6, GluR7, KA1, and KA2, which are structurally similar to AMPA and NMDA subunits of ionotropic glutamate receptors. KA1 and KA2 subunits can only form functional receptors with one of the GluR5-7 subunits. Moreover, GluR5-7 can also form functional homomeric receptor channels activated by kainate and glutamate when expressed in heterologous systems. Kainate receptors are involved in excitatory neurotransmission by activating postsynaptic receptors and in inhibitory neurotransmission by modulating release of the inhibitory neurotransmitter GABA through a presynaptic mechanism. Kainate receptors are closely related to AMAP receptors. In contrast of AMPA receptors, kainate receptors play only a minor role in signaling at synapses and their function is not well defined.